Step 1: Install MacPorts using the instructions from http://www.macports.org/install.php
Step 2: Update MacPorts
sudo port -v selfupdate
Step 3: Install Xcode command line tools from
Xcode->Preferences->Downloads->Command Line Tools
Step 4: Accept the xcodebuild license
sudo xcodebuild -license
Step 5: Install subversion
sudo port install subversion
The first time you install a package through MacPorts it will take a long time to build the standard libraries but the next package will install much more quickly.
When you want to upgrade any MacPorts packages that are out of date use:
sudo port upgrade outdated
The user guide for MacPorts can be found http://guide.macports.org/